214 THE HAEMOFLAGELLATES 



right (or dorsal) half is perceptibly smaller, but denser and more deeply 

 staining than the other. In this manner, therefore, two distinct nuclear 

 bodies are formed, of different size and character. They remain connected 

 together by a fine achromatic thread, representing the original central 

 spindle, which ends in a small granule near the centre of each. The 

 larger nucleus, lying nearer the middle of the body, rapidly reconstitutes 

 itself and enters upon a resting-phase. This nucleus regulates the trophic 

 functions of the cell, for which reason we have proposed (3) for it the 

 name trophonucleus. 



Meanwhile, the other, smaller nucleus proceeds to give rise to the 

 characteristic locomotor apparatus of the Trypanosome. It passes forwards 

 slightly and takes up a position at the periphery of the endoplasm, lying 

 indeed against the limiting ectoplasm. Its centrosome divides again in 

 a similar manner, forming another axial spindle (E, a.s 2 ) at right angles, 

 as before, to the length of the parasite. Another heteropolar division 

 next takes place, giving rise to two daughter-nuclei ; these also remain 

 connected together by the drawn-out central spindle, which join the two 

 centrosomic granules. The peripheral daughter-nucleus, situated almost 

 in the ectoplasm, forms yet another spindle (F, a.s 3 ), whose axis is now, 

 however, longitudinal. This assumes large proportions and spreads 

 forward to the anterior end of the body, the whole lying in the ectoplasm, 

 which becomes greatly developed to form the undulating membrane. 

 The central spindle becomes excentric in position and sinuous in outline, 

 and strengthens, or rather itself constitutes, the free edge of the membrane, 

 forming a flagellar border to it (H, /.&). A supporting framework is 

 formed by eight myonemes, representing the eight elongated daughter- 

 chromosomes, four of which are arranged on each lateral surface. The 

 flagellar spindle does not stop on reaching the anterior end of the body, 

 but continues to elongate, drawing out with it the undulating membrane, 

 which narrows and finally thins away. The myonemes then unite with 

 the spindle to form the free flagellum, the centrosome at the distal end 

 disappearing as such, but that at the basal or proximal end persisting (c). 

 By this time the other daughter-nucleus has become rounded off as the 

 kinetonucleus (k\ which regulates all the kinetic activities of the parasite ; 

 it remains connected with the locomotor apparatus by a delicate thread, 

 representing the second axial spindle. 1 



According to Prowazek's recent investigations, the same type of 

 nuclear structure is also shown by two Mammalian forms, T. lewisi 

 and T. brucii', indeed, it is maintained that the system of axial 

 spindles produced by successive divisions of the karyocentrosome 



1 Two other points bearing on the view that the flagellum represents the greatly 

 elongated axial spindle of a nuclear division may be noted. In Trypanosoma 

 johnstoni, where there is no free portion of the flagellum, this terminates (at the 

 limit of the cytoplasm) in a small deeply- staining granule (Fig. 34), perhaps com- 

 parable to the distal centrosome of such a spindle. Again, Miss Robertson (72) 

 sums up her account of the origin of the flagella in the development of the flagellate 

 form from the rounded, aflagellar type in the case of her leech - Trypanosome by 

 saying, "the two flagella appear to be developed from a pair of arrested mitotic 

 figures developed out of the distal of the two segments into which the original 

 kinetonucleus divides." 



